A seven-year review by the UK Government, led by the Zoological Society of London (ZSL), discovered that the number of cetaceans washed up on UK shores has increased. A total of 4,896 whales and dolphins have been reported stranded between January 2011 and December 2017 – 15% more than during the previous seven-year time period. With more than 1,000 reports, 2017 marks the highest stranding numbers in a single year since the start of the programme in 1990.
To identify the reasons behind the deaths, 1,030 post-mortem examinations were conducted. Amongst the leading causes, infectious disease and entanglement in fishing gear were found to be most common. One in four of the reported common dolphin deaths were accounted for by the latter – also known as bycatch – alone. Further reasons were ship-strikes, killing 25 animals, and death due to ingestion of marine litter.
Since diseases can often be associated with exposure to chemical pollution and prey depletion leading to malnourishment and a weakened immune system, cause of death in these instances can be mostly attributed to human activity.
However, ZSL cetologist Rob Deaville points out that the increase in number of strandings might also be due to less negative factors. Whilst “increases in local reporting effort” may be an influence, it could also stem from the long-term recovery of several cetacean populations. The collaborative UK Cetacean Strandings Investigation Programme (CSIP) recorded 21 different cetacean species in the same time period as the ZSL review, making up “nearly one quarter of all currently known species”. Including the sward sperm whale that has never been reported in UK waters before.
Further long-term monitoring and examination studies are ongoing with the intention to deepen our knowledge on the main causes of increased stranding numbers and mortality factors. This should result in means to mitigate possible deaths and to “gain a real insight into the wider health of the marine environment”.
For more information, see: https://biomeecology.com/research/2019/09/4896-marine-mammals-stranded-on-uk-coast-in-seven-years/
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